Flames of Desires
by Revamped Persona
Summary: Dying Will Flames are said to be fueled and controlled by the user's desire, so what if a certain soon to be mafia boss gains the powers of the Multi King? How would Vongola deal with the results of this event? (AU in which Tsuna becomes a Kamen Rider.)
1. Return and Reunion

**AN: Welcome to my very first Fanfic that I'm working on alone! I've been considering writing a fic where Tsuna becomes a Kamen Rider for a very long time. Today is the day where I finally get off my lazy ass and just do it! I'd really appreciate it if reviewers could give me some constructive criticism if I need to work on something. Ok now that that's out of the way, let's get the show on the road!**

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 **Prologue: The Selfless Boy and the Selfish Bird**

In the distance of a small town named Namimori, two people can be seen walking towards it. One of them was a small fourteen year old boy. His hair is a simple shade of brown and also appeared to be pretty fluffy. This chocolate brown eyed boy wore a simple

yetat the same time peculiar outfit. A pair of jeans and a poncho that was striped red, yellow, and green. The other man walking alongside the brunette appeared to be the exact opposite of him. This man had blond hair that was swept to the right, his eyes seemed to hold a much harsher look than the other's more innocent gaze as if they pierced through the soul. The blond wore a pair of red skinny jeans, and a black shirt with a white jacket casually draped over it. Strangely enough the right sleeve of said jacket had a red shorter sleeve that appeared to have been stitched on.

"Tch. I can't believe that you are willing to come back to this stupid town Tsuna." The blond sneered at his companion. The expression would've terrified the smaller male now revealed to be called Tsuna, but he at this point was very used to the other's jabs and spiteful remarks. "It's okay Ankh. I think that it's time I face my problems instead of running away." He answered to Ankh giving him a reassuring smile. The blond didn't share the same viewpoint that Tsunahad of the town. It was the place after all that nearly made Tsuna lose his desire.

Flashback: 2 1/2 Years Ago Sawada Residence

Sawada Tsunayoshi wasn't happy at all. He has been mercilessly bullied by his own classmates for years, yet it never seemed to relent. The brunette was also aware that he had a strange cold feeling in his chest. At first it didn't bother him when he was younger and the old man did something to him, but as the years passed it felt like something should be there yet it wasn't. Tsuna would've attempted to get some sort of help, but it would've been useless. His mother Sawada Nana was painfully unaware of her own son's life, and the less said about his father is better. Sawada Iemitsu barley visited his own family the last time that Tsuna remembered seeing his father, he mentioned something about going to do construction work with penguins.

Tsuna finally had enough of Namimori. He couldn't stand being in the town anymore and especially despised being called Dame Tsuna and secretly yearned to be free. Since Tsuna was fearful of seeing Nana's tearful face should he ask her, he decided to run off in the middle of the night. And so Tsuna waited until dark to begin his escape. When the sky turned the darkest shade it could, Tsuna slipped out of bed. He didn't bother taking much since all he really needed was a pair of clothes and some yen. The brunette began to take his bed sheets and tied them together. Next he tied one end of his makeshift rope to the leg of his bed. Finally he started to climb out of the window using the sheets to gently lower himself down. Once he was at ground level,Tsuna knew that he was going to have to be fast since leaving Namimori had one major obstacle. That said obstacle being one Hibari Kyoya.

Hibari was one individual that Tsuna avoided like the plague. Although he is slightly older than Tsuna himself, he was a very intimidating male. Hibari was in his own words a "carnivore" and if he finds a "herbivore" like Tsuna leaving Namimori, he'll most likely put him in the hospital. Tsuna made sure to keep his eyes everywhere in order to not be detected by the black haired demon. Finally Tsuna was at Namimori entrance and with a heavy heart, slipped out and began a journey that will impact what is to come years after...

* * *

Tsuna accompanied by Ankh were standing in front of the former's home. "This is your last chance Tsuna." The blond started to say. "If you want to turn back, then now is the time."

"I told you before Ankh. I'm ready to face my fears. I have no regrets about meeting her again." Tsuna answered. The brunette took a short glance at Ankh, and finally rang the doorbell.

"Coming~!" A cheerful voice chimed as the two heard footsteps nearing the door. As the knob turned and the door opened, The traveling pair met the face of Sawada Nana. The smile on Nana's face stopped as she laid eyes on the son that she thought wouldn't ever return.

"Ts-Tsu kun?" She started to say as tears were threatening to leak. Tsuna just gave a smile and said with more confidence then he had when he last saw her, "Hello Okaasan. I'm home." Nana wept as she finally latched onto her son and lead him and the stranger accompanying him inside.

After two and a half years of waiting, Sawada Tsunayoshi finally returned to Namimori. Nothing will be the same as Tsuna now wields an ancient power that was thought to have been a lost relic forgotten by time itself. And as the worlds of Flame and Medals meet, he'll be there reaching his hand out to those who desperately need it.

This is the story of Vongola X, Kamen Rider OOO!

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 **AN: Was it good? I don't mind getting some feedback about any of the fanfics I write. I feel that criticism is needed in order to improve any kind of art.**


	2. Enter Reborn!

**AN: Thanks you for the support you've given me. I know that the first chapter looks to be odd, but I have an explanation for it. You see I only have a small iPhone for now, and it's really hard editing and writing with one. I'm still trying to figure out what works. Once I get a better computer, it should be better and more consistent. I hope you like the longer chapter. Now onto the next chapter!**

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 **Chapter 1: What a Kamen Rider is a Mafia Boss?!**

Tsuna hadn't quite expected what was to come after he hugged his mother for the fifth time in a row. Ankh simply stood back grimacing as he watched the sickeningly sweet reunion in front of him. The blond was thinking about his opinions on Sawada Nana. "She's just as bad as Chiyoko." Ankh thought shivering as he realized what this could mean for himself. Ankh certainly did not want to deal with another Chiyoko. "I can't believe I'm sitting here watching this idiotic sappy garbage." The blond muttered under his breath. This however made Nana realize that Tsuna did not come back alone.

"Tsu-kun who is that man with you?" Nana questioned her son while staring at Ankh. The blond had his arms folded over his chest and was focused more on Tsuna than paying attention to Nana.

Tsuna himself did not know what to say. He couldn't just tell his own mother about Ankh since he isn't really a human. Ankh is a kaijin known as a Greeed a being that is hundreds of years old. When Tsuna first met him, Ankh was only just a red forearm with a bird motif. The two eventually were forced to make a tense partnership when a Yummy attacked looking for the core medals that Ankh had taken with him when he was awakened. Ankh himself explained to Tsuna that Greeed like himself are made up of countless cell medals, yet only the core medals were what keeps a Greeed alive similar to a popsicle on a stick.

Eventually though, Tsuna finally managed to give an explanation. "Okaasan this is my friend Ankh." He introduced the Greeed to Nana. "He helped while I was traveling." Ankh simply nodded in Nana's direction not bothering to smile or shake her outstretched hand. "Ankh isn't really much of a social person…" Tsuna nervously explained to a confused Nana. "He does like ice candy though."

Once introductions were over, Tsuna and Ankh went upstairs to sleep in Tsuna's unoccupied bedroom. The brunette slipped into the covers of his old mattress while the Greed quickly started to remake his nest that had been packed with him and made a makeshift hammock out of it. The two finally managed to drift into a dreamless slumber after what felt like hours. However as they were sleeping, Nana woke up and went to get the morning mail. All that was inside of the mailbox was a peculiar message. She took it out and read what seemed like a promising message.

"Will raise your child to be the leader of a new generation. Grade and subject doesn't matter."

-Reborn

From the shadows a small figure can be seen watching Nana walk back to the house. A smirk can be seen on his face. Oh he couldn't wait to 'tutor' his new student.

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Tsuna woke up as usual with Ankh already awake before him. The duo quickly moved downstairs to where Nana was preparing breakfast. Tsuna was careful to make sure that Ankh ate his meal instead of eating ice pops that were most likely paid by Tsuna himself. He still shuddered at the incident involving the eggs. "Tsu-kun Ankh-kun guess what?" Nana asked them both with an excited look on her face. Ankh simply tilted his head wondering what this woman was asking while Tsuna had an uneasy feeling. "I don't know Okaasan. Can you please tell us?" Nana seemed to become even more ecstatic as she finally revealed the answer. "I realized that since Tsu-kun missed over two years of school, he's fallen behind. That's why in addition to enrolling you in Namimori Middle, I also got you a home tutor to help you catch up on your grades!"

Tsuna nearly choked on the piece of toast he was chewing on while Ankh had a brief expression of shock before combing back to his usual one of indifference. "Hieee!" Tsuna cried. "N-no Okaasan. It's okay. I don't need a tutor. I've learned a lot on my own." Tsuna's attempts to call off the possibility of a tutor didn't work as Nana cut in. "But Tsu kun, he's already expected to arrive today." Now Tsuna was mentally panicking. He did not want a home tutor potentially learning about both his and Ankh's secrets. Unfortunately before Tsuna could try to change Nana's mind again, a small squeaky voice interrupted him. "Ciaossu." All three pairs of eyes turned to look at the newcomer. Oddly enough it was a baby no larger than Tsuna's foot dressed in a suit and fedora. A green chameleon could be seen on top of the orange banded hat as well as there being a gleaming yellow pacifier hanging around the child's neck. Ankh narrowed his eyes. This baby was dangerous. The Greeed could feel his cores screaming at him that this baby with something that needed to be watched. Ankh would be damned if he let that baby harm Tsuna.

"I am the home tutor Reborn." The baby started to speak. "My job is to tutor Sawada Tsunayoshi." This exclamation got hold of both Tsuna and Ankh's attention. They both didn't want this baby tutor to be around them since something was clearly off about Reborn. Tsuna especially didn't like the maniacal gleam in the toddler's onyx eyes.

"Tch. There is no way in hell that I'm letting you near Tsuna!" Ankh spat in Reborn's direction. "You'd have to get past me first, and I'm very hard to kill." The Greeed finished his remark with a wicked smirk on his face. This however did the opposite of what Ankh was intending. Reborn is very hard to intimidate. As such, it merely made him interested in Ankh. Reborn was convinced at first that Ankh was a civilian. Iemitsu's notes never mentioned any blondes hanging around Tsuna before, so it was assumed that he is a civilian. Now that he was meeting Ankh in person however, the assumption was fading away and he knew that the Young Lion of Vongola will be receiving a bullet in the knee very soon. Luckily before the two could inflict any damage on each other, Tsuna already dragged Ankh outside claiming that they need to know the layout of Namimori. However neither of them noticed who was following them.

Namimori Shrine: Noon

"Ankh why did you do that?" Tsuna scolded at the blond with an upset look. "Tch. That baby isn't normal baka!" Ankh retorted. "That baby is unnatural, and it's messing with my cores. I can't feel what that thing desires at all. It's as if there's a force field keeping what he wants away from me."

"Eh? You couldn't feel his desire Ankh?" Tsuna questioned. This never happened before. Normally Ankh is able to feel and tell what people desire because of his inhuman origins. Something was wrong if a Greeed couldn't decipher what Reborn desired the most. "How are we going to deal with Reborn if we don't know anything about him?" Tsuna mentally pondered. Maybe they had no choice but to use-

"Ciaossu!" Reborn was standing on top of Tsuna's head even though he wasn't there a minute ago. The baby lazily kicked his feet on top of the brunette's fluffy hair.

"How the fuck did you find us?!" Ankh snarled. He was about to lash out in anger, but Tsuna knowing the other's habits managed to stop him by grabbing his right arm. "Let go of me baka!" Ankh raged while thrashing in Tsuna's arms. "I will kill him!"

Reborn however wasn't afraid in the slightest. In fact he appeared to be amused by the Greeed's threats. "Oh. You plan to kill me?" He taunted. "How are you going to do that? I am after all the number one Hitman in the mafia."

Ankh paused in Tsuna's grip not expecting to hear such an asinine statement. "Tsuna this brat is clearly fucking insane." The Greeed wanted to be nowhere near this kid. "I say we kill him and let him rot." Tsuna however wasn't going to let Ankh do what he wanted. "Ankh no. We've already talked about not killing people." The brunette was trying to protect Reborn from Ankh, yet in reality it was Ankh who needed protection from Reborn.

Reborn suddenly jumped off Tsuna's head as the chameleon on top of his fedora changed into a gun without warning. "I'm the Katekyo Hitman Reborn, and I am here to make Dame Tsuna a mafia boss no matter the cost." The baby cocked his gun. "Many tried to kill me, yet none of them ever succeeded. How can you of all people even land a scratch on me?"

Ankh finally had enough as an idea suddenly came to him. "Oi Tsuna. Get the belt." The order sounded odd to anyone who didn't understand what it meant, but to Tsuna and Ankh that 'belt' was their means of survival.

Reborn could only watch as his supposed student took out an odd looking buckle that wrapped around his waist. The belt had three round slots and a round device hanging off of the side. "Ankh are you sure that this is a good idea?" Tsuna whispered in the Greeed's ear. "That baby is not normal. It is probably a kaijin in disguise." Ankh hissed under his breath. "Now just transform already and beat the shit out of him!"

Tsuna sighed. He could ignore what Ankh was saying, but he too had the feeling that Reborn wasn't normal either. Whenever he looked at the tutor's eyes, the black orbs made him shiver. Turning to face Reborn Tsuna started to insert three medals into the slots. "I'm sorry about what I'm going to do Reborn." The red medal with a hawk slid in. "Normally I wouldn't do this, but Ankh has a point." The yellow medal that had a tiger engraved on it went in next. "If, you really are a kaijin in disguise, then it's my job to defeat you." The final medal green with a grasshopper etched on the surface was placed in the last remaining slot. "I'll make sure that everyone is safe even if it means that I have to fight!" Tsuna unclipped the circular device and swiped it across the medals and shouted the one word that will forever change the Vongola family.

" _HENSHIN_!"

 **TAKA!**

 **TORA!**

 **BATTA!**

 **TA-TO-BA! TATOBA! TA-TO-BA!**

Without hesitation three circular symbols lit up and flew around Tsuna. As the jingle finished the three symbols lined up the red hawk on top, the yellow tiger in the middle, and the green grasshopper on the bottom. The symbols combined into one and landed on Tsuna's chest creating armor.

The armored figure that Tsuna had transformed into was a strange sight, yet colorful at the same time. The suit was mainly black, but there were many lines running across it. The legs were green and were reminiscent of an insects. The middle half was yellow and appeared to loosely resemble a tiger's. Tsuna's head was covered by a helmet that bore the image of a red bird. The helmet also bore green lenses that resembled an insects. Finally there was a logo on the chest of the armor. It was of a red hawk, yellow tiger, and green grasshopper.

"Dame Tsuna just what is that armor?!" Their opponent questioned. Reborn never expected this of all things to have happened. First a man named Ankh is with him and now his student uses a belt to transform into the armored figure before him. It was at this very moment that Reborn realized that Iemitsu screwed up royally and will pay for his mistakes.

"My name is Sawada Tsunayoshi, but right now I'm Kamen Rider OOO!" The newly dubbed OOO exclaimed. "I don't know what you want with me, but I know that I have to fight!" OOO rushed towards Reborn as the baby Hitman prepared himself for a fight against his new student.

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 **AN: Yup! I'm finally back updating and revising this fic after over a year of an unexplained absence. I was actually trying to finish up high school and was way too preoccupied with that to add more to this fanfic. Now that I'm back though after finally graduating, I've got much more to do. Get ready for more exciting Kamen Rider fanfics and more!**

 ** _Now let's see some of the reviews I got during my hiatus..._**

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 **foxchick1**

Thanks for reading my story! I really appreciate the nice comments you posted. There will definitely be some good surprises in the future.

 **yoga pratama**

Sorry, but that probably won't happen. As of right now, it's the equivalent of a Level 50 character facing a Level 100 boss in an RPG. Tsuna would have to get stronger to defeat Reborn and even then it's unlikely.

 **Hikari Nova**

Thanks for the correction. I hope that this is much better now. And yeah… Kamen Rider's got some pretty corny moments, but I still adore the franchise.

 **Nightmare WingXFallen Tenshi**

I didn't know that you were this pumped about my fanfic. It reminds me of myself. Don't worry, I won't let this fanfic or any future fanfics that I write, die. I always keep my promises, even the silent ones


	3. Two Worlds Clash

**AN: Well, welcome back to Chapter 3! I probably will disappoint somebody with how I handle a fight between OOO and Reborn… but I stand by what I think is the most realistic outcome should this scenario ever happen in real life.**

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 **Chapter 3: OOO's Return**

Reborn quickly threw himself to the right as OOO attempted to gain the upper hand. The infant carefully looked at the Kamen Rider, checking for any weak points that he could potentially expose. Finally figuring out a strategy after a second, Reborn used the green gun that Leon had become to rapidly shoot bullets at OOO. OOO not expecting such a fast response, faltered a bit getting hit with a few of the bullets, but managed to use his grasshopper legs to jump out of the way before the majority could hit him.

Reborn smirked as he had his wayward student right where he wanted him.

Before OOO could properly move out of the way, Reborn suddenly changed the angle of his shots and this time couldn't get out of the way. In less than a second, he felt pain coursing throughout his entire body. " _AGH_!" OOO cried out in pain, as each bullet met its target.

"TSUNA!" Ankh shouted, "CATCH!" And he grabbed two new medals out from a black box like container with light blue markings. Throwing the medals as hard as he can, they quickly shot past Reborn and landed upon Tsuna's waiting palm.

 **TAKA!**

 **UNAGI!**

 **CHEETAH!**

Although there was no additional tune, the armor swapped to a blue torso with whip like extensions on the arms and yellow spotted legs. The helmet remained the same. Using the new arm extensions, OOO quickly swung over to a tree. However he used the momentum of the swing to fling himself back at Reborn, kicking the small hitman using the Cheetah legs. However, the toddler wouldn't go down so easily. Just as he was about to make contact with the wall of the temple he was about to be thrown into, Reborn used his foot to bounce off of the wall using the force from the bounce to send OOO a roundhouse kick.

This time, OOO was the one who was slammed through the wall and just as he was about to get up, Reborn landed on his chest. "Are you done?" The baby questioned him. Though it sounded more like an order as the gun was aimed right at his head.

"He's not done yet, asshole!"

Before Reborn could turn around, Ankh appeared out of nowhere, his right forearm now a bright crimson bird like arm. The feathers were beautiful, the many colors looked as if they are gleaming in the sunlight. Using his inhuman appendage, Ankh managed to get a hold of Reborn gripping him within his taloned grasp. Ankh smirked. He _knew_ that the "baby" hadn't been expecting this. Kaijin weren't really a common sight to see unless you lived in Japan.

"Had enough?" He taunted, watching Reborn struggle for a bit. Normally he wouldn't act _this_ sadistic, but this time was a special case. Tsuna is the only person that Ankh felt like he could trust. He wasn't using him for his own gain or selfish intentions. All that the small boy wanted was a friend. Ankh refused to let him die. He would protect the younger's innocence even if it killed him a second time.

Tsuna himself didn't know what to do. On one hand the infant that claimed to be his "tutor" had just tried an attempt on his life, but on the other Ankh would surely kill Reborn. Tsuna didn't want Ankh to become a killer. No one should succumb to that bloodlust. Tsuna finally decided that he had to stop this.

"W-wait! Ankh STOP!" He yelled running towards his friend. Clinging onto the same arm that was being used to choke the life out of Reborn. Ankh tensed, not ready to let go, but Tsuna managed to pry the hand open giving Reborn an opportunity to break free. The hitman used the squabble as the perfect distraction he needed. Reborn slammed his foot on Ankh's head knocking him down. As Ankh fell, Reborn quickly shot Tsuna in the chest where OOO' symbol is located. As OOO fell on the ground, the symbol grayed out and the transformation cancelled, reverting OOO back to Tsuna.

"Now then…" Reborn started to say, the gun transforming back into the lizard before crawling back on top of his hat. "I was sent here by the orders of Vongola Nono to train "Dame" Sawada Tsunayoshi into becoming the next boss of the Vongola family."

Tsuna started to sweat as the hitman kept going. "I've been observing you ever since you returned to Naomori. You wouldn't think that I, the greatest hitman in the world wouldn't notice _any_ out of place information?" Ankh huffed as he carefully started standing up, checking to make sure no cell medals were shaken loose out of him. "The documents that were given to me are worthless. There was nothing about a person named "Ankh" neither was it known that Dame Tsuna had run away from home for years. I am especially lacking any information of Sawada Tsunayoshi becoming a "Kamen Rider"..." Reborn sharply turned to face Tsuna, his onyx eyes locking onto Tsuna's chocolate orbs.

"I guess that I'll have to write new records about you during my time as your tutor." Tsuna stammered, still not wanting the baby near him. "Shut up Dame Tsuna, a mafia boss doesn't cry." Reborn said calmly, kicking Tsuna head in the process.

Tsuna cried out, but Ankh quickly caught him before he could completely fall. "What the hell are you doing?!" the Greeed spat, shooting daggers at Reborn.

"Teaching." Was the only response he got.

Both Tsuna and Ankh had a bad feeling as they were forcibly lead back to the Sawada household.

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It was a large room with clean floors and white walls. In front of a large glass window was a brown desk the shade of darkest bark. A man could be seen sitting right at the desk's head, his face appearing to gleam with the sheer amount of joy on his face. Just as he was about to speak, the door opened a brunette woman walked in wheeling in… a cake?

"Happy Birthday to you…" The man sung, placing the dessert on the desk. The cake was a simple vanilla cake, but the top was decorated with three familiar red, green, and yellow symbols. The man kept singing the familiar childish tune as he cut the cake, the woman beside him sighing as she watched.

"Happy Birthday to you… OOO!"

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 **AN: Yup! I'm baaaaaaaack! I really did think of whether or not Reborn could beat OOO, but I think that Tsuna isn't experienced enough to beat a professional hitman like Reborn. I did consider the full combos, but do you really think that Tsuna would whip those out right away? Those are his aces in the hole. Besides, the combos are destructive and take a lot out of the user. Maybe Tsuna could potentially beat Reborn in the future, but it's highly unlikely as of right now.**


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